Page:NIOSH Manual of Analytical Methods - 9109.pdf/7

 METHAMPHETAMINE. . . on Wipes by SPE: METHOD 9109, Issue 1, dated 17 October 2011 - Page 7 of 33

V4 =	 volume in mL of desorbate actually taken for extraction and diluted to 5 mL with blank desorbing solution containing internal standard. b =	 concentration in media blank (in µg/sample determined from the calibration curve).

V5 = volume correction factor for the media blank (needed only if the volume of internal V2 standard spiking solution used for spiking the media blank is different from that used for spiking the calibration standards). V5 =	 volume in µL of internal standard spiking solution used to spike media blank. 20.	Report concentration, C’, in µg per total area wiped (in cm2) as follows:

C’=

C A

C = µg/sample (step 19). A = Total area wiped in cm² per sample. NOTE: In general, if the area wiped was greater than or less than 100 cm², do not convert value to μg/100 cm² unless specifically required or allowed by agency having legal jurisdiction. For example, if the sample was a composite sample and the area was 400 cm², report results as μg/400 cm² and not averaged to μg/100 cm² since regulatory agencies might not allow averaging of composite results to 100 cm². To avoid confusion, report separately both μg/sample (C) and the total area wiped in cm² per sample (A) for both discrete and composite samples. EVALUATION OF METHOD: This method was developed according to the NIOSH sampling and analytical method development guidelines. [2] This method was evaluated for those analytes listed in Tables 8a and 8b over a range of approximately 0.1 μg/sample to 30 μg/sample for several types of sampling media. These concentration levels represent approximately the 1 through 300 times the limit of quantitation (LOQ) level for most of the analytes. Results are reported in the Backup Data Report [1]. The limits of detection (LOD and LOQ) were determined by preparing a series of liquid standards in desorption solution, processing by the SPE of NIOSH 9109, and analyzing in the scan mode. The LODs were estimated using the procedure of Burkart [9]. An LOD of 0.1 μg/sample for methamphetamine on wipes was achieved in the scan mode. The LOD was set at 0.1 μg/sample because that was the level of the lowest calibration standard in the LOD/LOQ study. Lower LODs (e.g., 0.02 μg/sample) have been achieved in practice by including calibration standards at lower concentration levels. The cleanliness and performance of the mass spectrometer must be maintained such that at 0.1 μg/sample a signal of at least 5 to 10 times the baseline noise is achievable. This is more easily accomplished in the SIM mode. Six different wipe media were evaluated. These were 3”x3” (7.5 cm x 7.5 cm) 12-ply cotton gauze, 4”x4” (10 cm x 10 cm) AlphaWipe® (TX 1004), 4”x4” (10 cm x 10 cm) 4-ply NU GAUZE®, 4”x4” (10 cm x 10 cm) 4-ply MIRASORB®, 4”x4” (10 cm x 10 cm) 6-ply SOF-WICK®, and 4”x4” (10 cm x 10 cm) 4-ply TOPPER® sponges. Results are given in the Backup Data Report [2]. No synthetic media performed better than cotton gauze. Some media (NU GAUZE® and SOF-WICK®) gave inconsistent results.

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

Method rev. 1.1.1